Hello, it is recommended that you use secret messages to encrypt the mail client. You just need to log in to your email account. Secret letter App automatically applies for e-mail encryption certificate and signature certificate, automatically deploys and configures e-mail certificate, automatically exchanges public keys of encryption certificate, automatically encrypts and signs each e-mail by default, automatically stamps each e-mail, automatically decrypts encrypted e-mail, and automatically updates expired encryption certificate and signature certificate. More importantly, the signing certificate and encryption certificate of V 1 automatically configured by default are completely free.